The preparation of polyether carbonate polyols by catalytic reaction of alkylene oxides (epoxides) and carbon dioxide in the presence of H-functional starter substances (“starters”) has been the subject of intensive study for more than 40 years (e.g. Inoue et al., Copolymerization of Carbon Dioxide and Epoxide with Organometallic Compounds; Die Makromolekulare Chemie 130, 210-220, 1969). This reaction is shown in schematic form in scheme (I), where R is an organic radical such as alkyl, alkylaryl or aryl, each of which may also contain heteroatoms, for example O, S, Si etc., and where e, f and g are integers, and where the product shown here in scheme (I) for the polyether carbonate polyol should merely be understood such that blocks having the structure shown may in principle be present in the polyether carbonate polyol obtained, but the sequence, number and length of the blocks and OH functionality of the starter can vary, and is not limited to the polyether carbonate polyol shown in scheme (I). This reaction (see scheme (I)) is environmentally very advantageous since this reaction constitutes the conversion of a greenhouse gas such as CO2 to a polymer. A further product, actually a by-product, formed is the cyclic carbonate shown in scheme (I) (for example, when R═CH3, propylene carbonate).

EP-A 0 222 453 discloses a process for preparing polycarbonates from alkylene oxides and carbon dioxide using a catalyst system composed of DMC catalyst and a cocatalyst such as zinc sulfate. This polymerization is initiated by a one-off contacting of a portion of the alkylene oxide with the catalyst system. Only thereafter are the remaining amount of alkylene oxide and the carbon dioxide metered in simultaneously. The amount of 60% by weight of alkylene oxide compound relative to the H-functional starter substance, as specified in EP-A 0 222 453 for the activation step in examples 1 to 7, is high and has the disadvantage that this constitutes a certain safety risk for industrial scale applications because of the high exothermicity of the homopolymerization of alkylene oxide compounds.
WO-A 2003/029325 discloses a process for preparing high molecular weight aliphatic polyether carbonate polyols (weight-average molecular weight greater than 30 000 g/mol), in which a catalyst from the group consisting of zinc carboxylate and multimetal cyanide compound is used, this catalyst being anhydrous and first being contacted with at least a portion of the carbon dioxide before the alkylene oxide is added. Final CO2 pressures of up to 150 bar place very high demands on the reactor and on safety. Even the extremely high pressure of 150 bar resulted in incorporation of only about 33% by weight of CO2 up to a maximum of 42% by weight of CO2. The accompanying examples describe the use of a solvent (toluene) which has to be removed again by thermal means after the reaction, thus resulting in increased time and cost demands. Furthermore, the polymers, with a polydispersity of 2.7 or more, have a very broad molar mass distribution.
WO-A 2008/092767 discloses a process for preparing polyether carbonate polyols, characterized in that one or more H-functional starter substances are initially charged in the reactor and in that one or more H-functional starter substances are metered continuously into the reactor during the reaction. This process thus has the drawback that one or more H-functional starter substances have to be initially charged in the reactor.
European patent applications having application numbers EP12181907.2 and EP12181905.6 disclose processes for preparing polyether carbonate polyols by addition of alkylene oxides and carbon dioxide onto one or more H-functional starter substance(s) in the presence of a double metal cyanide catalyst, characterized in that suspension media containing no H-functional groups are initially charged in a reactor and one or more H-functional starter substance(s) are metered continuously into the reactor during the reaction. EP12181907.2 additionally discloses that it is possible here to add small amounts of phosphoric acid (e.g. 90 ppm of 85% H3PO4) to the starter substance metered in continuously (e.g. glycerol).